Study On Several Key Techniques For Improving Performance Of Spectral Domain Optical Coherence Tomography

Optical coherence tomography (OCT), as a new imaging technique, has great potential in clinical medicine due to its non-invasion, non-radiation, high resolution and high sensitiveness. OCT is traditionally considered as Time-domain OCT (TDOCT). It needs depth scanning of reference arm. Different depth corresponds to different depth information of the sample. However, the collection time is limited by depth-scanning with no further application in vivo. Spectral-domain OCT (SDOCT) uses spectrometer instead of photoelectric cell, and it able to obtain the whole depth information through Fourier Transform of the collected interference spectrum. The system is more simple and steady under a higher speed. In order to apply high speed OCT in more fields, the imaging quality, the imaging speed, the signal to noise ratio, the axial resolution and several other key techniques are studied in this paper.The research mainly includes:1. Scattering signals are classified into two categories according to One Order Born Approximation and multiple scattering theory. The simulation results on the basic of SDOCT Monte-Carlo module indicate that the second category photons have wider spatial and angular distribution, and the phenomenon explains why SDOCT is likely to be implemented. The number of emitting photons of TDOCT are much lager than that of SDOCT under the coherent condition, however the imaging speed is much slower, for the axial scanning is carried out in the TDOCT, and the scanning point is located in the same layer of media, it is a problem needed to be solved by TDOCT to get an actual and meaningful position to improving scanning efficiency. In order to resolve the problem of gray scale's degression of layers in the media, Monte-Carlo simulation is adopted.2. Mathematical model of SDOCT is set up to obtain image function and then the principals and image structures of SDOCT are analyzed. The Phase shift spectral domain OCT, the phase difference OCT and the complex spectral OCT all manage to enhance image quality, and make the full range measurement possible. Two step phase shift method is adopted to speed up the measurements and the result tells us that it is more efficient than conditional five step phase shift method.3. A new interferometer with special coating beam splitter is designed to manage to enhance the image quality. The design reduces the intensity in reference arm to 25 times less than before and lessens the energy gap between two arms. The image contrast goes up to 100 times more than before. Meanwhile, signal to noise ratio improves by 6dB.4. In order to restrict the linear phase shift error, two methods (spatial domain and time domain) are applied to study the phase shift method. They have the same result: five step phase shift method is the optimal image construction method. It has little influence on the image structures, restricts more for the mirror image and the full range measurement is implemented.5. To improve the axial resolution and signal to noise ratio of SDOCT image, a new measurement of coherent length and axial resolution is brought forward in the paper. Zero-padding technique is used to compensate the degression of axial resolution induced by nonlinear phase shift error. White spectral OCT is set up on partial spectrum analysis,the system chooses required white light source and receiving spectral. It would have more detection depth, higher resolution and improving signal to noise ratio.